Method and apparatus for making electric heaters

ABSTRACT

An improved method, and apparatus, for forming strip heaters wherein the heating resistor is disposed in centered relation within a cake of compressed refractory material in a single operation. The invention includes a cavity in a mold in which the resistor is supported on winding pegs and electrically connected to terminals. The base of the sheet metal channel of the heater to be formed is placed in juxtaposed relation with the cavity opening, and this base is pressed toward the cavity to compress refractory material and a binder within the cavity. The winding pegs are withdrawn from the mold cavity during the pressing operation to strip the resistor therefrom and leave the latter centered in the compressed cake of refractory material contained within the heater channel.

United States Patent Unger et al.

[451 Oct. 10,1972

[ METHOD AND APPARATUS FOR MAKING ELECTRIC HEATERS [72] Inventors: Robert W. Unger; Wallace H. Sunderman, both of Pittsburgh, Pa.

[52] US. Cl. ..29/61l, 29/613, 29/615, 29/203 R, 264/109, 425/117, 425/123 [51] Int. Cl. ..H05b 3/00 [58] Field of Search ..29/61l, 610, 614, 615, 613, 29/203 R; 264/109, 110, 111; 141/12;

1,903,604 4/1933 Wiegand ..29/6l5 Primary Examiner-John F. Campbell Assistant Examiner-Victor A. Di Palma AttorneyMichael Williams [57] ABSTRACT An improved method, and apparatus, for forming strip heaters wherein the heating resistor is disposed in centered relation within a cake of compressed refractory material in a single operation. The invention includes a cavity in a mold in which the resistor is supported on winding pegs and electrically connected to terminals. The base of the sheet metal channel of the heater to be formed is placed in juxtaposed relation with the 125/117 123 cavity opening, and this base is pressed toward thecavity to compress refractory material and a binder [56} References Cited within the cavity. The winding pegs are withdrawn from the mold cavity during the pressing operation to UNITED STATES PATENTS stripdthe resistor therefrom land eavfe; the latter ceni tere in the compressed ca e 0 re actory materia l i contained within the heater channel. 1,821Z822 9/1931 Wiegand ..29/6l5 11 Claims, 7 Drawing Figures PATENTEDncI 10 1912 SHEET 1 0F 2 T. R E 1 w w mk ILI METHOD AND APPARATUS FOR MAKING ELECTRIC HEATERS BACKGROUND AND SUMMARY Insofar as is know, electric heating elements of the strip heater type are still being manufactured by a process generally disclosed in U.S. Pat. No. 1,903,604, issued to Edwin L. Wiegand. As disclosed in this patent, the heating resistance is wound on pegs which extend from the side surface of a support. The support is bounded by side walls which thus forms an opensided cavity. Granular refractory material and a suitable binder are pressed into the cavity to cake form and the cake is removed from the cavity with the resistance conductor in part visible from a side of the cake. This side of the cake is then placed face up in the sheet metal channel of the heater to be formed, and further granular refractory material and suitable binder are placed over the cake and compressed so that the heating resistor is fully encapsulated. The sides of the channel are then formed inwardly over the cake, or over a metal plate overlying the cake, to complete the assembly.

Although the foregoing method of making a strip heater has been commercially successful for many years, it has certain disadvantages in that the two step method necessary to completely encapsulate the heating resistor not only required additional time and labor but also the bond between the two cake sections does not always result in the required homogenity.

The present invention overcomes the above disadvantages in that the heating resistor is completely encapsulated in a single operation and therefore the principal object of the present invention is to provide new and improved methods of and apparatus for producing electric heating elements of the character described.

DESCRIPTION OF THE DRAWINGS In the drawings accompanying this description and forming a part of this specification, there is shown, for purpose of illustration an embodiment which this invention may assume and in these drawings:

FIG. 1 is a top plan view of apparatus embodying this invention,

FIG. 2 is a sectional view generally corresponding to the line 2-2 of FIG. 1,

FIG. 3 is an enlarged sectional view corresponding generally to the line 3-3 of FIG. 1,

FIG. 4 is a fragmentary perspective viewof a detail,

FIG. 5 is an enlarged fragmentary sectional view showing parts in position prior to a pressing operation,

FIG. 6 is a view similar to FIG. 5 with parts in position after the pressing operation, but before the heater is stripped from the mold, and

FIG. 7 is a fragmentary perspective view of a strip heater, ready for final assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENT posite ends of the side plates and are connected thereto. An anvil, or mold 14 is rigidly secured between the side plates 11 by means of bolts 15. The anvil corresponds in dimensions generally to the dimensions of the sheet metal channel 16 (see FIGS. '5 and 6) of the strip heater to be produced, as seen in FIG. 3, opposite sides of the anvil are undercut to provide elongated recesses 17 for receiving respective legs 18-18 of the sheet metal channel 16.

Heads 19 and 19.1 are disposed between the side plates 1111 at opposite ends of the anvil for vertical sliding movement relative thereto. The heads 19, 19.1, and a further head 19.2, extend upwardly from and are secured to a support plate 20 which is disposed between the side plates l1--11. The heads 19 and 19.2 slidably engage the end plates 12-12 to longitudinally locate the support plate 20. The upper part of the anvil 14 is recessed, as seen at 21, and this recess, in combination with the heads 19,191, define the mold cavity 22. The upper sides of the cavity are completed by elongated strips 22.1 (see FIG. 3) which are removably attached, as by pins (not shown) to the upper surfaces of the side plates 1 1-l 1.

The heads 19, 19.1 may be attached to the support plate 20 by screws (not shown) which pass through openings in the plate and are threaded into respective heads. Provision is made to vary the length of the strip heater to be produced by the improved apparatus and, as shown in FIG. 1, the plate 20 is formed with sets of openings 20.1 spaced in a direction toward the head 19.2. If a strip heater is to be produced which is longer than the setting of the heads l9,19.1 shown in FIG. 1, the head 19.1 is released from its position and moved to the right to alignment with a selected set of holes, and the screws reinserted to hold the head 19.1 in the adjusted position. The anvil 14 is replaced by one of a length to span the heads 19, 19.1 in such adjusted position of the latter. For the longest length of strip heater which may be produced, the head 19.1 is removed entirely, and an anvil of a length to span the heads l9,l9.2 is utilized.

The support plate 20 rigidly carries a pair of pins 23 which extend upwardly therefrom and freely into openings in the anvil, the upper ends ofthe pins terminating below the flat base 21 of the anvil, and forming a retractable abutment engageable with the lower end of the shank 24 of terminal pins 25 (see FIG. 5). A second support plate 26 is disposed below the support plate 20 and it rigidly carries a plurality of winding pegs 27 which extend upwardly therefrom and freely through openings in the support plate 20 and anvil l4.

Coil springs 28 are disposed between the upper surface of the base 10 and the undersurface of the support plate 20 to urge the latter to its upper position defined by abutment with the lower edges of the end plates 12. As best seen in FIGS. 5 and 6, rods 29 are disposed within the respective springs 28, the lower end of each rod being rigidly connected to the base 10 and upper end extending freely through openings in the support plates 20, 26. The rods hold the springs 28 in place and also assist in guiding movement of the support plates 20, 26.

Lighter coil springs 30 are disposed between the upper surface of the base 10 and the undersurface of the support plate 26 to urge the latter to its upper position. Rods 31 are disposed within the respective springs 30, the lower end of each rod being rigidly connected to the base and the upper end extending freely through respective openings in the support plate 26.

As seen in FIG. 5, in the upper positions of the support plates 20, 26, the heads 35 of the terminal pins 25 are disposed above the cavity 22 and so are the reduced, upper ends 36.1 of the winding pegs 27. A coiled resister wire 36 is wound about the pegs 27 and has its opposite ends connected to the terminal pins 25 as suggested by the dot-dash lines in FIG. 1. As seen in FIG. 5, the resistance wire is disposed in the upper portion of the mold cavity 22, and the latter is filled with granular refractory material 38 mixed with a binder, the upper surfaces of the strips 22.1 providing guide means for a scraping tool to level the refractory material. As suggested in FIG. 5, the refractory material surrounds the resistor wire 36 and those parts of the terminal pins 25 and winding pegs 27 which are located in the mold cavity.

The sheet metal channel 16 of the strip heater to be produced is disposed in inverted relation over the mold cavity so that its base 39 is aligned with the cavity and overlies the same. An opening 40 in the channel base may receive a pin 41 on the head 19 to align the channel longitudinally of the mold cavity. The channel is pressed downwardly against the refractory material so that the legs l818 enter the longitudinally extending recesses 17 at opposite sides of the upper end of the anvil, or mold 14, and the strips 22.1 are then removed.

The apparatus thus far described is placed in a suitable press, with the base 10 supported on the fixed platen (not shown) of the press. The movable platen 45 of the press (see FIG. 6) is then lowered to press against the base 39 of the heater channel 16 and to force the same toward the mold cavity to compress the refractory material therein; As the channel base 16 is pressed downwardly, the heads 19, 19.1 and 19.2 and support plate 20 move downwardly in unison therewith. Downward movement of the support plate 20 causes retraction of the pins 23 carried thereby and thus removes support for the terminal pins 25 so that the latter are moved by compressing action of the refractory material to a centered position relative to the cake of compressed refractory material, as seen in FIG. 6.

The winding pegs 27 are also moved downwardly to a position wherein their upper ends are removed from the mold cavity, as seen in FIG. 6, so that the resistor wire is stripped from the pegs and left in centered position in the compressed cake. As best seen in FIGS. 2 and 4, the support plate 26 for the winding pegs 27 is moved downwardly at a variable rate in order to accomplish proper centering of the resistance wire. Each end of the support plate 26 is bifurcated, as seen at 50 in FIG. 4, and an end 51 of a lever 52 is freely movable between the furcations of the support plate 26. The opposite end 51a of the lever is pivotally carried by a block 53 (see FIG. 2) which is rigidly connected to the base and extends upwardly therefrom.

The ends of the furcations of the support plate are formed with lands 54 against which blocks 55 hear. The blocks 55 are pivotally carried from opposite sides of the lever 52, as best seen in FIG. 4, and intermediate the ends of the lever. A bolt 56 (see FIG. 2) is threaded through the support plate 20 and its lower end is adapted to bear against the upper surface of lever leg 51. A second bolt 57 is threaded through the support plate 20 at a position outwardly of the bolt 56 and its lower end is adapted to bear against an undercut upper surface 58 of the lever leg 51a. In the upper position of the support plate 26, the lower end of the bolts 56 bear against the upper surface of corresponding lever legs 51, while the lower ends of the bolts 57 are spaced a slight distance (about 0.080 inches in the disclosed embodiment) from the surface 58 of lever leg 51a.

Referring to FIG. 2, the distance a between the center of bolt 56 and the pivot of blocks 55 is about equal to the distance a between the pivot of blocks 55 and the pivot for lever end 5 la. Thus, as support plate 20 is moved downwardly by pressing force against the heater channel base 39, the plate 26 will initially be moved downwardly half the amount through action of the bolt 56 bearing against the lever end 5l.-l-Iowever, this condition exists only for a short time before the lower end of the bolt 57 engages the lever surface 58 to shorten the swinging radius of the lever 52 and thereby multiply the downward rate of movement of the support plate 26. In the illustrated example, the distance b is about one-half the distance a (see FIG. 2) so that the support plate 26 is then moved at about twice the rate of the support plate 20 to quickly remove the upper ends of the winding pegs 27 from the mold cavity to a lower position shown in FIG. 6, leaving the resistor in centered position within the compressed cake of refractory material.

With both support plates 20, 26 in the lower position shown in FIG. 6, a latch end 60 (see FIG. 3) ofa lever 61 engages over the upper surface of plate 26 to hold the same in its lower position to prevent the winding pegs from elevating and injuring the compressed cake of refractory material when the upper platen 45 of the press is elevated clear of the channel base 39. The coil springs 28 will elevate the support plate 20 and the heads 19 and 19.1 and/or head 19.2 to strip the heater assembly from the mold cavity.

Figure 7 shows the heater channel 16 with the compressed cake of refractory material therein, and with the channel inverted from the position it assumed on the mold. A sheet metal closure plate 65 is provided to complete the strip heater assembly, this plate having openings 66 to pass the shanks 24 of the terminal pins, and insulating bushings (not shown) disposed over the shanks, and the legs 1818 of the channel 16 are folded inwardly to lock the closure plate 65 in place and deformed to close the ends of the channel. As seen in FIG. 7, the channel legs 18 have notches 67 to clear the terminal shanks 24.

We claim:

1. The method of forming an electrical heating element of the strip heater type which has a sheet metal channel at least in part enclosing the heating resistance and the insulating material therefor, comprising disposing terminal pin means and winding peg means in a mold cavity which is of dimensions corresponding to that of said channel, winding a resistance wire around said peg means and in electrical circuit with said terminal pin means, and extending flatwise of but spaced from the bottom of said cavity, placing granular refractory material and a binder in said cavity to substantially fill the same, disposing the sheet metal channel of the strip heater to be formed over said mold cavity with the inner surface of the base of the channel in juxtaposition relative to the cavity, and pressing the base of said channel toward said mold cavity, to compress the refractory material therein while withdrawing said peg means from said cavity to strip said resistance wire therefrom.

2. The method of forming an electrical heating element of the strip heater type which has a sheet metal channel at least in part enclosing the heatingresistance and the insulating material therefor, comprising disposing a pair of terminal pins and at least two winding pegs within the cavity of a mold which has dimensions corresponding to said channel, supporting said terminal pins and pegs to extend transversely of the base of said cavity, winding a resistance wire around and between said pegs and terminals and extending flatwise of but spaced from the bottom of said cavity, placing granular refractory material and binder in said cavity to substantially fill the same, disposing the sheet metal channel of the strip heater relative to said cavity so that the inner surface of the channel base is in juxtaposition with respect to the cavity opening, pressing said channel base toward said cavity to compress the refractory material therein, and withdrawing the support of said terminal pins and winding pegs as said channel base compresses said refractory material.

3. The method of claim 2 wherein the support of said terminal pins is withdrawn at a rate uniform with the pressing movement of said channel base.

4. The method of claim 2 wherein the support of said winding pegs is initially withdrawn at a rate proportional to the initial pressing movement of said channel base and thereafter is withdrawn at a faster rate.

5. The method of claim 4 wherein the support for the winding pegs is withdrawn at said proportional rate for only a very short period as compared to the withdrawal at said faster rate.

6. The method of claim 2 wherein the support for said terminal pins is withdrawn at a rate uniform with the pressing movement of said channel base, and wherein the support of said winding pegs is initially withdrawn at a rate of about half the initial pressing movement of said channel base and thereafter is withdrawn at a faster rate.

7. Apparatus for encapsulating the heating resistance of a strip heater in refractory material in the sheet metal channel of the heater, comprising a mold having a cavity of dimensions corresponding to those of the channel of the heater to be formed with opposite sides of the cavity open, means for supporting a pair of terminal pins and at least two winding pegs within said cavity for movement transverse to the base of the same, a resistance wire wound around said pegs and electrically connected to said terminal pins and extending flatwise of but spaced from the cavity base, granular refractory material and a binder within said cavity and substantially filling the same and surrounding said resistance wire and the inner ends of said terminal pins and winding pegs, a sheet metal channel of a heater to be formed having its base rectilinearly aligned and in juxtaposition with the cavity opening and its legs adapted to fit on opposite sides of said cavity, means for pressing said channel base toward said cavity to compress the refractory material therein, the inner extremities of said terminal pins being moved transversely of said cavity base to substantially centered position by said compressing action, and means operative during the pressing operation to withdraw said winding pegs from said mold cavity to strip the resistance wire therefrom and leave the same substantially centered within and encapsulated by the compressed refractory material.

8. The apparatus of claim 7, including a support for the outer ends of said terminal pins, said support being movable in the same direction as and uniformly with the means for pressing the channel base toward said cavity to thereby withdraw support of said terminal pins during compression of said refractory material.

9. The apparatus of claim 7, including a support for the outer ends of said winding pegs, said support being movable in the same direction and initially at about half the rate of movement of the means for pressing the channel base toward said cavity, and means for the thereafter increasing the rate of movement of the winding pegs support during pressing action of said refrac tory material.

10. The apparatus of claim 9, including a movement leverage system operable to move said winding pegs support at said half rate for only a short period of time as compared to the increased rate of movement.

1 1. The apparatus of claim 7, including means for increasing the length of said mold cavity.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION P t N 3 696 507 Dated October 10 1972 Inventor(s) Robert Unger a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 1, "know" should read known Column 2, line 4, after "produced" remove the comma and add As Column 6, line 37, remove "the" at the end of the line, so that the line reads "channel base toward said cavity, and

means for".

Signed and sealed this 13th day of February 1973.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents USCOMM-DC 60376-P69 fr us. GOVERNMENT PRINTING OFFICE: [969 0-366-334.

FORM PO-1050 (10-69) 

1. The method of forming an electrical heating element of the strip heater type which has a sheet metal channel at least in part enclosing the heating resistance and the insulating material therefor, comprising disposing terminal pin means and winding peg means in a mold cavity which is of dimensions corresponding to that of said channel, winding a resistance wire around said peg means and in electrical circuit with said terminal pin means, and extending flatwise of but spaced from the bottom of said cavity, placing granular refractory material and a binder in said cavity to substantially fill the same, disposing the sheet metal channel of the strip heater to be formed over said mold cavity with the inner surface of the base of the channel in juxtaposition relative to the cavity, and pressing the base of said channel toward said mold cavity, to compress the refractory material therein while withdrawing said peg means from said cavity to strip said resistance wire therefrom.
 2. The method of forming an electrical heating element of the strip heater type which has a sheet metal channel at least in part enclosing the heating resistance and the insulating material therefor, comprising disposing a pair of terminal pins and at least two winding pegs within the cavity of a mold which has dimensions corresponding to said channel, supporting said terminal pins and pegs to extend transversely of the base of said cavity, winding a resistance wire around and between said pegs and terminals and extending flatwise of but spaced from the bottom of said cavity, placing granular refractory material and binder in said cavity to substantially fill the same, disposing the sheet metal channel of the strip heater relative to said cavity so that the inner surface of the channel base is in juxtaposition with respect to the cavity opening, pressing said channel base toward said cavity to compress the refractory material therein, and withdrawing the support of said terminal pins and winding pegs as said channel base Compresses said refractory material.
 3. The method of claim 2 wherein the support of said terminal pins is withdrawn at a rate uniform with the pressing movement of said channel base.
 4. The method of claim 2 wherein the support of said winding pegs is initially withdrawn at a rate proportional to the initial pressing movement of said channel base and thereafter is withdrawn at a faster rate.
 5. The method of claim 4 wherein the support for the winding pegs is withdrawn at said proportional rate for only a very short period as compared to the withdrawal at said faster rate.
 6. The method of claim 2 wherein the support for said terminal pins is withdrawn at a rate uniform with the pressing movement of said channel base, and wherein the support of said winding pegs is initially withdrawn at a rate of about half the initial pressing movement of said channel base and thereafter is withdrawn at a faster rate.
 7. Apparatus for encapsulating the heating resistance of a strip heater in refractory material in the sheet metal channel of the heater, comprising a mold having a cavity of dimensions corresponding to those of the channel of the heater to be formed with opposite sides of the cavity open, means for supporting a pair of terminal pins and at least two winding pegs within said cavity for movement transverse to the base of the same, a resistance wire wound around said pegs and electrically connected to said terminal pins and extending flatwise of but spaced from the cavity base, granular refractory material and a binder within said cavity and substantially filling the same and surrounding said resistance wire and the inner ends of said terminal pins and winding pegs, a sheet metal channel of a heater to be formed having its base rectilinearly aligned and in juxtaposition with the cavity opening and its legs adapted to fit on opposite sides of said cavity, means for pressing said channel base toward said cavity to compress the refractory material therein, the inner extremities of said terminal pins being moved transversely of said cavity base to substantially centered position by said compressing action, and means operative during the pressing operation to withdraw said winding pegs from said mold cavity to strip the resistance wire therefrom and leave the same substantially centered within and encapsulated by the compressed refractory material.
 8. The apparatus of claim 7, including a support for the outer ends of said terminal pins, said support being movable in the same direction as and uniformly with the means for pressing the channel base toward said cavity to thereby withdraw support of said terminal pins during compression of said refractory material.
 9. The apparatus of claim 7, including a support for the outer ends of said winding pegs, said support being movable in the same direction and initially at about half the rate of movement of the means for pressing the channel base toward said cavity, and means for the thereafter increasing the rate of movement of the winding pegs support during pressing action of said refractory material.
 10. The apparatus of claim 9, including a movement leverage system operable to move said winding pegs support at said half rate for only a short period of time as compared to the increased rate of movement.
 11. The apparatus of claim 7, including means for increasing the length of said mold cavity. 